Applies to new inductive voltage transformers for use with electrical measuring instruments and electrical protective devices at frequencies from 15 Hz to 100 Hz. Relates basically to transformers with separate windings, but is also applicable, where appropriate, to auto-transformers. Covers requirements and tests, that are necessary for single-phase inductive protective voltage transformers. Includes requirements which apply particularly to transformers which are required to have sufficient accuracy to operate protective systems at voltages that occur under fault conditions. Replaces the second edition of IEC 186 (1987), its amendment 1 (1988) and amendment 2 (1995) only as far as the inductive voltage transformers are concerned. IEC 186 remains in force for the capacitor voltage transformers.